1. Field of the Invention
The present invention relates to a probing apparatus, and more particularly to a probing apparatus capable of probing a micro signal from a measured device disposed on an insulated substrate that mounts a plurality of devices spaced apart from each other.
2. Description of the Related Art
Production of a liquid crystal display includes patterning a plurality of transparent electrodes on a glass substrate and, if necessary, further includes forming circuit elements, such as transistors, diodes, resistors, and capacitors, on the glass substrate. In order to improve productivity, plural liquid crystal display blocks are disposed in a predetermined pattern on the same glass substrate. Forming the plural liquid crystal display blocks are performed as a single process by means of a photolithography technique or the like. For example, a square or rectangular glass substrate having one side exceeding 1 m is used. A total of 100 or more liquid crystal display blocks, each having one side of several cm, are disposed in a predetermined pattern on the glass substrate.
Inspection of a glass substrate mounting liquid crystal display elements thereon is performed with a probing apparatus and a tester, at appropriate timing, during or after production. In this case, a method similar to an IC measurement method which is well known conventionally can be used for inspecting the characteristics of a device formed on a glass substrate. More specifically, device measurement on a glass substrate requires a probing apparatus and an appropriate measuring apparatus connected to the probing apparatus. The probing apparatus includes a stage for supporting and shifting the glass substrate to an arbitrary position, a contact or non-contact probe for inputting or outputting a measurement signal to or from a measurement terminal of each display element on the glass substrate, and a connecting portion that connects the probe to a measuring unit.
The measurement performed by the probing apparatus includes, in a simple case, a test for a wiring pattern to be internal opened or internal shorted (open-short circuit test), or, in a complex case, an operation characteristic test for respective transistors and a turn-on operation test for the liquid crystal display. For example, Japanese Patent Application Laid-open No. 11-65475 discloses a probe apparatus that uses an XY stage for supporting a display panel and measures characteristics of the display panel by means of a probe.
The characteristic measurement of a device on a glass substrate, especially measurement of transistor characteristics on a liquid crystal display or measurement of holding capacitance of each pixel which provides a potential to an ITO (Indium Tin Oxide) electrode in each pixel circuit, is a low-current measurement. Therefore, if large internal (or external) noises are present, sufficient measurement accuracy will not be assured. Hence, shielding a space including both the stage and the probe is used.
However, when a large-scale glass substrate is used to form plural devices thereon as described above, a large shielding space is required to cover a moving range, or a shifting range of the stage in addition to the entire area of the glass substrate. For example, when the glass substrate is a square substrate having one side of 1 m, the stage requires a shifting range of extra 1 m in both the X and Y directions. As a whole, a required shielding area is equivalent to a square area having one side of 2 m.
As is understood from the foregoing description, according to a conventional technique, a probing apparatus for a large-scale glass substrate mounting a plurality of devices requires a further larger shielding facility. As a result, both the size and the cost of the probing apparatus inevitably increase.